Yep, what Oops said.... This is a Bevis valve. I broke mine aways back and spliced the line together. As I remember looking up the specs, it opens around 100 degrees. Living in Phoenix, I figured mine was open most of the time anyway...... I picked on up at You Pull it for 2 bucks but it's a ***** to get to, so i'll replace it the next time the intake is off.
I've noticed no difference without it.